Various turning angle detectors are proposed. Some of the detectors are shown in FIGS. 14 and 15.
FIG. 14 schematically shows one of the turning angle detectors at a turning angle of 0 degree. This turning angle detector includes a rotor J3 and a stator J6. The rotor J3 includes two generally semi-cylindrical yokes J1 and two magnets J2. The rotor yokes J1 are made of magnetic material. Each end of each rotor yoke J1 is spaced with a magnet arrangement gap from one end of the other yoke J1. Each rotor magnet J2 is positioned in one of the magnet arrangement gaps between the rotor yokes J1. The poles of the two rotor magnets J2 are oriented in the same direction.
The stator J6 is surrounded by the rotor J1 and includes two cores J4 and two Hall ICs J5. The stator cores J4 are generally semi-columnar and made of magnetic material. The flat surfaces of the stator cores J4 define a magnetism detection gap between them. The Hall ICs J5 are positioned in the magnetism detection gap. Each Hall IC J5 is an IC including a Hall device incorporated into it, which is a magnetism sensing element.
FIG. 15 schematically shows another turning angle detector at a turning angle of 90 degrees. This turning angle detector includes a rotor J3 and a stator J6. The rotor J3 comprises two semi-cylindrical magnets J2 so that magnetic flux passes from one of the rotor magnets J2 to the other. The stator J6 is surrounded by the rotor J3 and includes two cores J4 and two Hall ICs J5. The stator cores J4 are generally semi-columnar and made of magnetic material. The axial flat surfaces of the stator cores J4 define a magnetism detection gap between them. The Hall ICs J5 are positioned in the magnetism detection gap.
FIG. 16A shows the relationship of typical turning angles to the density of the magnetic fluxes through the Hall ICs J5 (hereinafter referred to magnetic flux density) in each turning angle detector.
If the magnetic flux density changes in a sine curve with respect to the turning angles, the density change has a deviation characteristic, which is indicated by the broken line A in FIG. 16B, with respect to the ideal line (ideal magnetic flux density) that is the linearized density change. As indicated by the broken line A, the magnetic flux density drops greatly at turning angles of 60 and more degrees, so that the detectable angle range is narrow.
Therefore, the outside shape of the stator cores J4 and/or the inside shape of the rotor yokes J1 are varied so as to increase the magnetic flux density in the vicinity of the turning angle of 90 degrees, thereby widening the detectable angle range.
In FIG. 14, the rotor yokes J1 are generally elliptic so as to increase the magnetic flux density in the vicinity of the turning angle of 90 degrees, thereby widening the detectable angle range (for example, Patent Document 1).
In FIG. 15, the semi-cylindrical rotor magnets J6 are radially magnetized so as to increase the magnetic flux density in the vicinity of the turning angle of 90 degrees, thereby widening the detectable angle range (for example, Patent Documents 16 And 3).
[Patent Document1]
U.S. Pat. No. 6,476,600 (JP-A-2001-317909)
[Patent Document 2]
JP-A-2001-208510
[Patent Document 3]
U.S. Pat. No. 6,356,073 (JP-A-2001-188003)
In order to detect turning angles of the rotor J3 accurately from the magnetic flux density, it is necessary to linearize the change characteristic of the magnetic flux density in the detectable angle range.
As stated above, each of the turning angle detectors is so constructed that the magnetic flux density in the vicinity of the turning angle of 90 degrees is high for a wide range of detectable angles. As indicated by the solid line B in FIG. 16B, the change characteristic of the magnetic flux density in the devised detector has a deviation varying with respect to the ideal line and increasing remarkably around a turning angle of 70 degrees. Consequently, it is impossible to linearize the change characteristic in a wide range.
Therefore, the outside shape of the stator cores J4 and/or the inside shape of the rotor yokes J1 may be so varied as to linearize the deviation when the rotor J3 is positioned between its turning angles of about 70 and 80 degrees. In this case, as shown in FIG. 16C, the characteristic line (ultimate line) drops sharply at turning angles of 80 and more degrees, so that the detectable angle range is narrow.